This invention relates to an improved foundation unit for supporting a mattress of the like and, more particularly, a foundation unit with a resilient border and a center that is firmer than conventional torsion spring-type units and yet is sufficiently resilient to support a body on an overlying mattress comfortably.
It generally desirable to have a firm surface for sleeping or reclining upon and many improvements have been made in the structure of mattresses to provide such a firm surface. The underlying foundation unit also contributes to the degree of firmness of the mattress sleeping surface, but also must protect the mattress from damage due to ordinary and/or unusual use. Mattresses generally include an innerspring assembly consisting of a plurality of coil springs which can be damaged or crushed under unusual loads, if not provided with an underlying structure that has a sufficient degree of resiliency to absorb such crushing pressures. For instance, if a mattress containing coil springs with four or five convolutions per spring (the most common type of mattress) is supported by a rigid surface or platform, it will suffer an extreme amount of wear because it has no underlying structure to absorb some of the loads to which it is subjected. It is therefore desirable to provide a foundation unit that contributes to the firmness of a mattress sleeping surface and is sufficiently resilient to protect a mattress during normal and extraordinary uses, such as from a person sitting at the edge of the mattress.
Foundation units are generally formed of a wooden, rectangular frame which is transversed by a series of cross rails positioned near the bottom of the unit, which rails support a plurality of torsion springs or the like. The torsion springs are secured at their lower ends to these cross rails while the upper portion of the torsion springs supports the upper surface of the unit. The upper surface of the unit generally includes some insulating material and a decorative covering which is extended down the sides of the unit and secured to the bottom of the frame. The upper surface can also include a wire grid underlying the insulating material, which grid may be secured to the torsion springs below.
Such a foundation unit, which includes torsion springs throughout its structure, does protect a mattress from unnecessary damage but does not contribute to the firmness of the entire assembly to the extent desired. The most important area to which a foundation unit can contribute firmness is the center region upon which a body will most frequently be reclined. It is desirable to provide a foundation unit which will contribute firmness to the overlying mattress sufficient to support a reclining body with its spine in a straight position and this requires that the assembly be sufficiently resilient to conform to the body's shape and yet not allow portions of the body to sag.
Apparatus for supporting mattresses which are simply frames with cross slats or the like are known in the art, for example as disclosed in U.S. Pat. No. 2,638,606. It is also known in the art to cushion such slats with devices such as an overlying foam pad as disclosed in U.S. Pat. No. 3,554,745. Such supporting devices, however, do not provide firm center support while maintaining sufficient flexibility for comfort. It is also known from U.S. Pat. Nos. 3,935,605 and 4,012,802 that a foundation unit can have a rigid center portion and a peripheral resilient area wherein the center region is substantially unyielding under normal loads. These foundation units would be too rigid to provide a comfortable degree of flexibility and damage-preventing support for the average innerspring assembly of a mattress.
It is desirable to provide a foundation unit for a mattress or the like which is firmer than a torsion spring unit about the center region while being sufficiently flexible to reduced damage to the overlying mattress and allow a comfortable degree of resiliency. It is also desirable to provide a foundation unit which includes a border region of greater resiliency than the center region to reduce damage from crushing loads to the overlying mattress due to the extraordinary use often encountered about the border region from common practices such as sitting on the edge of the assembly. It is also desirable to provide a foundation unit which has a secondary flexing mechanism to protect an overlying mattress by absorbing in part extraordinary loads or impacts. It is also desirable to provide a foundation unit assembly wherein a degree of firmness about the center region can be varied as desired by simple alterations of one or more variables in the construction without changing the design of the unit or method of assembly.
It is therefore an object of the invention to provide a foundation unit with a center region firmer than conventional torsion spring units while maintaining the degree of resiliency provided by torsion springs along the border or edge areas where the overlying mattress receives more frequent heavy loads which could crush the mattress edge if the underlying foundation was not resilient. It is also an object to provide a unit with a sufficient degree of resiliency about the center region to support a reclining body on an overlying mattress so that the spine of the reclining body is in the preferred straight position. A further object is to provide a foundation unit in which the degree of center firmness may be changed as desired by manipulation of one or more variables of the materials of construction without redesigning the unit or altering the method of manufacture.